Downhole operations involving the pumping of oil are used to suck or otherwise lift fluids such as oil from subsurface formations to the surface after the initial pressure from the subsurface formations has subsided.
In the oilfield industry, many wells use a downhole reciprocating type production pump to lift oil from a borehole to the surface. Rods extend from the surface to the extraction area to enable a pump jack located at the surface to cause reciprocal movement of the rod and bring oil to the surface. These rods are known as sucker rods or pump rods and are typically between 25 and 40 feet in length, and threaded at both ends. These rods join together the surface and downhole components of a reciprocating piston pump installed in an oil well. These rods are typically between 25 and 30 feet (7 to 9 meters) in length, and threaded at both ends.
For various reasons, such as wear and tear, and the accumulation of contaminants in a downhole environment, the sucker rods, their couplings, and downhole rod pumps must be removed and replaced from time to time. Typically, upon removal, these oilfield tools are subjected to various forms of inspection, reconditioning and or remanufacturing. In this manner, a used oilfield tool or its components can be safely returned to service.
In general, the main process of reclaiming or reconditioning a used oilfield tool utilized in oil pump wells comprises obtaining the tool, cleaning the rod to remove contaminates from use in oil extraction, and performing an inspection of the tool to determine if the tool should be reconditioned or discarded. In the case of sucker rods, the rods are categorized into steel class, heated until plastic deformation, shaped, cooled and cut to the desired length.
When these components are removed from the well and reclaimed, reconditioned or both, the general method includes cleaning the tool to remove contaminates from use in oil extraction, performing a visual inspection of the tool and gauging the tool to determine if the rod should be reconditioned.
Typical contaminants found on downhole rod pumps include scale, paraffin, and asphaltenes. When the used oilfield tools are removed from the wellbore, they undergo a cleaning process. Typically, the cleaning process entails washing, pressure washing or dipping the oilfield tool in kerosene, or other organic compounds such as mineral spirits, naptha and the likes to dissolve the contaminants on the equipment. However, the use of these chemicals, especially when heated, can release volatile organic compounds. This is problematic not only for the environment but for workers at facilities where the contaminants are removed.
After cleaning, the oilfield tools are visually inspected for defects as well as subjected to non-visual inspection techniques to ensure that there are no stress fractures and the like that could otherwise not be seen.
It would therefore be advantageous to reduce the contamination to the environment and to the cleaning facility by the utilization of non-toxic cleaners and cleaners which do not result in solubility of contaminates from rods such as sucker rods. Cryogens such as dry ice and non-toxic gases in low temperature liquid form could therefore be used to eliminate the problem of volatile organic compounds and reduce cleanup costs associated with using these organic solvents.
Because there is no secondary waste stream, non-toxic inorganic cryogenic liquids are advantageous from a cleaning standpoint. Typically, the only waste to clean up afterward is the grime, paraffin, scale, asphaltenes or whatever other contaminants were removed. Likewise, in the process of putting the tools back in service, total job time is greatly reduced due to the fact there is very little post-blast cleanup required.
Cryogenic applications to the surface of sucker rods can produce an expansion factor upon making contact with the rods themselves. This is because the cryogens liquids or solids can change and expand to a gas.
In the case of a propelled cryogen or cryogenic compound, depending on the type of cryogen being used, and the air pressure and nozzle selected, the cryogen can travel at speeds between 600 and 800 feet per second. Assuming that the cryogen is able to initially penetrate the contaminant, this expansion occurs at the underlying substrate, thus lifting the contaminant off. Alternatively or additively, the cryogenic liquid can produce a thermal shock effect, as the particles are at sub-zero temperatures.
Cryogens impacting a sucker rod or other pump rod surface with contaminants typically removes contaminates in one of three ways: via kinetic energy, via thermal shock or via a thermal-kinetic effect. Kinetic energy transfers the energy of the accelerated cryogen (or cryogenic compound) as it hits the surface of the rod to be cleaned during the blasting process; this is akin to a pressure washing effect. However, in some applications, a low pressure cryogenic liquid is instead used. Likewise, thermal shock occurs when certain cryogens strike a much warmer contaminated surface during the blasting process. The cold temperature of the cryogen causes the bond between the surface being cleaned and the contaminants to weaken. This effect aids in the release of the contaminant when struck by the liquid during the blasting process. The thermal-kinetic effect combines the impact of evaporation and the rapid heat transfer discussed above. When the pressurized cryogenic liquid hits the contaminated surface, the vapor expands fast enough that micro-explosions occur which take off the contaminants from the rod.
In other situations, a cryogen or cryogenic compound can be used as a bath. As explained above, used oilfield tools are often bathed in organic solvents such as heated kerosene baths. Instead, it would be advantageous to dip or bathe the contaminated oilfield tools in cryogenic liquids such as liquid nitrogen, cryogenic solid pellets such as dry ice, or cryogenic slurries comprising a gas in cryogenic liquid form mixed together with dry ice pellets. This last method, combined with agitation of the slurry or the oilfield tool would both allow thermal shock and a kinetic effect of bombardment with dry ice. The effect could also be achieved by adding other solid particles into the cryogenic liquid.
In the embodiments herein discussed, the non-toxic inorganic cryogenic liquids are gasses which liquefy below the freezing point of water. Preferable examples of non-toxic liquids with an evaporation point below the freezing point of water which can be utilized in the present invention include: liquid nitrogen, liquid oxygen, liquid hydrogen, liquid helium, liquid neon, liquid argon, liquid krypton, liquid xenon, sulfur hexafluoride, and the like.